The present invention relates generally to a rotor assembly for an internal combustion engine, and more particularly to a single piece machined rotor or flywheel assembly with a plurality of magnets and spacers mounted thereto and a method of reducing the labor and cost of manufacturing a rotor for various types of engines using a permanent magnet ignition and/or charging system.
The present invention relates generally to an electrical system for an internal combustion engine, and more particularly to a charging system for a small internal combustion engine.
The electrical system of a small internal combustion engine typically comprises an ignition system and a charging system. The electrical system can be designed to produce either alternating current (AC) or direct current (DC). If the vehicle does not include a battery, an alternator of the electrical system operates like a generator, generating AC power as long as the engine is running. If the vehicle includes a battery, a rectifier is coupled to the alternator to convert AC power to DC power so that it can be stored in the battery and used to supply power to accessories even when the engine is off. Engines that operate at high speeds also generally require a regulator to maintain a steady voltage output.
The ignition system is responsible for starting the engine. Whether the engine is started with a tug on a rewind rope or by the turn of a key on an electric starter motor, the ignition system produces a spark inside the combustion chamber of the engine. The ignition system is coordinated with the timing of the piston and the motion of the valves so that the spark will ignite the air-fuel mixture in the combustion chamber just as the piston reaches the point of maximum compression in each engine cycle. Once the engine is running, the flywheel's inertia keeps the engine crankshaft spinning until the piston's next power stroke, while the flywheel magnets keep inducing a current in the armature to keep the spark plug firing.
The charging system is responsible for keeping the battery charged for starting the engine and powering the electrical accessories on a vehicle. When the engine starts running, the charging system takes over. The charging system becomes responsible for supplying energy to all of the loads when the engine is running and recharging the battery.
Typical charging systems include an ignition switch, an alternator, a rectifier, a regulator and a battery. When the ignition switch is in the ON position, the battery current energizes the alternator. The alternator generates and delivers electrical power to the battery and the rest of the electrical system. The alternator typically includes a stator and a rotor. The stator generally includes a plurality of windings wound around a plurality of poles extending outwardly from a core. The stator is mounted under the rotor with the rotor having a plurality of magnets mounted in the inside surface of the sidewall of the rotor. Rotation of the rotor creates a magnetic field and induces a current in the windings of the stator. On some engines, the stator includes an adjustable armature mounted outside of the rotor that relies on the same magnets as the ignition armature to charge the battery. The battery supplies all of the electrical power during cranking and when the engine is off. The rectifier converts AC power from the stator to DC power for charging the battery. The regulator maintains a steady voltage output.
Current methods for manufacturing a rotor for various types of engines are to machine a hub, stamp out an outside shell and fasten the components together. Most typical prior art rotor assemblies generally have a plurality of parts that require many steps in manufacturing and connecting the parts together. The prior art manufacturing methods include die casting, forming, stamping, and injection molding, which all require very expensive tooling and labor for assembling and fastening the multi-part rotor assemblies together.
FIGS. 1–3 illustrate an embodiment of a prior art rotor assembly 10 manufactured using expensive tooling, injection molding and other processes for constructing a multi-part rotor assembly. This prior art rotor assembly has a plurality of parts. A hub 12 is typically machined from a piece of steel. A stamping die is used to form an outside shell 14. The hub 12 is fastened to the outside shell 14 by rivets. A finishing machine is typically used to remove the rivet heads and smooth the surface of the rotor assembly. Magnets 16 are affixed to the inner surface of the outside shell 14 by an adhesive. A magnetic holding fixture is needed to hold the magnets in place around inner surface of outside shell 14 while the adhesive is curing. An injection molding machine is used for overmolding the magnets 16 to the outside shell 14, forming an injected molded part 24 in the outside shell 14. Overmolding is a process in which an elastomeric material is injected onto a product after the shell is produced. An embossing die may be used for forming ignition triggering protrusions 26 on the outer surface of the outside shell 14. Changing the size and diameter of the rotor assemblies would require additional tooling.
FIGS. 11–13 illustrate another embodiment of a prior art rotor assembly 20 with an engine speed sensor ring 18 fastened to the bottom of the hub 12 with fasteners 28. The hub 12 is fastened to the outside shell 14 by rivets. Magnets 16 are affixed to the inner surface of the outside shell 14 by an adhesive. An injection molding machine is used for overmolding the magnets 16 to the outside shell 14, forming an injected molded part 24 in the outside shell 14. An embossing die may be used for forming ignition triggering protrusions 26 on the outer surface of the outside shell 14. The speed sensor ring 18 typically includes a plurality of timing teeth 22 of various configurations that are used for engine speed sensing.
Therefore, a need exists for an integral rotor assembly that is easier and less expensive to manufacture. The present invention provides an integral machined rotor assembly for use on various types of engines having a permanent magnet ignition and/or charging system. The integral rotor assembly of the present invention can be incorporated into a plurality of different power equipment internal combustion engines which require battery charging and/or electrical power generation.